This invention relates to nuclear reactor pressure vessels and more particularly to a tool used to install O-ring seals in the removable head of a reactor pressure vessel.
In a typical nuclear reactor system that uses pressurized water as a coolant, the reactor vessel includes a removable upper steel head. The steel head when removed, provides access to the interior of the reactor vessel for purposes of refueling the reactor core, as well as any other required maintenance purposes. The removable head is secured to the body of the reactor vessel by a plurality of stud bolts and nuts installed around the circumference of a flange around the base of the removable head and a cooperating reactor vessel body flange. Since the reactor vessel is filled with pressurized water as a coolant during operation, it is necessary to provide a watertight, leakproof seal between the cooperating surfaces of the removable head flange and the reactor vessel body flange.
The seal typically includes a pair of hollow, metallic O-rings as gaskets placed within a pair of concentric circular grooves machined in the bottom flange surface of the removable head. These O-rings are circular metal tubes which resist the internal pressure of the coolant in cooperation with the bolted joints between the removable head flange and the reactor vessel body flange. The outside diameter of the O-rings is made slightly larger than the depth of the grooves machined in the bottom flange surface of the removable head. In this arrangement, when the removable head flange is bolted to the reactor vessel body flange, the O-rings are slightly flattened within their respective grooves by the smooth, flat surface of the reactor vessel body flange. The O-rings are also self-energized by permitting the internal pressure in the vessel to act on the inside of the metal O-rings through a series of slots formed in the O-ring. The double O-ring and bolted flange design of the reactor vessel have proven to be very effective in preventing any leakage of the pressurized coolant from the vessel during its operation.
The O-rings have been generally secured within the circular grooves machined in the bottom flange of the removable head by special clips. U.S. Pat. No. 4,980,117 to Ronald M. Blaushild discloses one type of clip used to secure the O-rings in place. As discussed in U.S. Pat. No. 4,980,117, the O-rings are replaced each time the vessel is opened for refueling or other maintenance purposes. When the vessel is opened and the removable head raised, the underside surfaces of the removable head defines an irradiated environment that could be hazardous to the maintenance personnel. To protect these maintenance personnel, it is desirable that the O-ring seals be replaced quickly and easily with a minimum exposure time to the irradiated undersurface of the removable head. In the past, replacement of the O-rings has required a number of maintenance personnel to properly support and position the O-rings while the retaining clips are installed and thereby increasing the risk of exposure to the irradiated environment under the head as well as the risk of working under suspended heavy steel structure.